gistfile1.py

#!/usr/bin/env python

version_elements = [
    '1',
    '12',
    '1a',
    '12abc3d4ef',
]

def foo(x, y):
    if isint(x[-1]) != isint(y):
        y = '.' + y
    return x + y


def isint(n):
    try:
        int(n)
        return True
    except ValueError:
        return False

for x in version_elements:
    print reduce(foo, x)